Conventionally, in order to guarantee network service level agreements (SLAs) it is often desirable to know the latency for a given service or link. This has typically been critical in higher latency store and forward packet technologies—namely Internet Protocol (IP), Ethernet and Multi-Protocol Label Switching (MPLS). For example, an IP network will use Ping and Trace-route to determine latency; other methods involve time stamped probe packets, or marking protocol data unit (PDU) overhead for real time measurements. Because of the intrinsic low latency and deterministic routing in optical transport networks such as G.709 Optical Transport Network (OTN) and SONET/SDH, measuring real time latency has been historically less critical than in high latency packet networks. Conventionally, the static nature of these networks allows a network operator to enter the latency for a link upon provisioning and typically no further updates are required on that link for the life of the network.
Most in-situ latency measurements are packet based. Latency measurements for SONET/SDH and OTN (TDM) networks has typically been pre-calculated based on topology, physical distance, or pre-determined using external measuring equipment. This method has been sufficient for time division multiplexed (TDM) networks when the topology is static or deterministic. In self healing mesh networks however, in particular hierarchical mesh networks, the topology can change. For example, optical switching at the Dense Wave Division Multiplexed (DWDM) layer, or OTN server layer can result in a new latency value. Since it is impractical to measure the latency for all possible paths in the network, a method of in-situ measurement that can measure the latency for any path is desired.